In color photography, images are produced by a color dye which is formed by the coupling reaction between the oxidized product of an aromatic primary amine color developing agent and a coupler. With multi-color photographic elements, a color image is usually produced by the subtractive color process, and the dye formed by the coupling reaction is typically a cyan, magenta or yellow dye which is produced in a silver halide emulsion layer or a layer adjacent thereto, said silver halide emulsion layer having sensitivity to the wavelength region of specific light to be absorbed by the image forming dye, namely, the red, green or blue region of the spectrum.
Pyrazolone couplers are commonly used as the magenta dye forming coupler, but they have low maximum color density and sensitivity, and absorptions other than the predominant one which are undesired. Furthermore, these couplers do not have sufficient long-term stability, and in particular, they are low in resistance to formalin and experience appreciable change in color and decrease in color formability.
In order to eliminate these defects, several proposals have been made. Japanese Patent Publication No. 30895/1973 shows a 1H-pyrazolo(3,2-c)-s-triazole magenta coupler having no undesired absorption other than the predominant one. However, with this coupler, little improvement has been achieved with respect to maximum color density, sensitivity and resistance to formalin.
Japanese Patent Publication No. 16058/1974 shows a bis-pyrazolone magenta coupler. This coupler has some improvement in sensitivity and formalin resistance, but not in maximum color density. Japanese Patent Public Disclosure No. 135841/1981 shows a 1H-pyrazolo(3,2-c)-s-trizole magenta coupler having its 1-position substituted by an active point in a compound having an active methylene group. This coupler is somewhat improved in formalin resistance, but not in maximum color density or sensitivity. Japanese Patent Public Disclosure No. 42045/1983 shows the use of a coupler having a terminal hydroxyphenylene sulfonyl group for the purpose of providing an improved maximum color density. However, the obtained maximum color density is not as high as desired.